Field of the Invention
The invention relates to a method and a device for safeguarding or protecting against penetration by foreign bodies into a roller nip, more particularly, between two cooperating cylinders, such as a contact-pressure roller cooperating with a plate cylinder in a printing press, in a manner that an automatically or semiautomatically supplied printing plate is mounted error-free on the plate cylinder and, in particular, a canted or bent trailing edge of the printing plate is introduced into a clamping and/or lock-up device for the printing plate.
A device of this general type has become known heretofore from the published German Patent Document DE 42 18 602 A1. In this known device, a contact-pressure roller corresponding in length to the length of the plate cylinder is provided, and is positionable against the plate cylinder by spring force. The spring force is applied by spiral compression springs, which have force action lines extending virtually radially to the plate cylinder. This known device has a protective function, in that a foreign member, such as a finger or hand, which may accidentally slip in between the contact-pressure roller and the plate, can displace the contact-pressure roller counter to the spring force of the spiral compression springs. A switch lever is connected to the contact-pressure roller via the shaft of the contact-pressure roller and, whenever the contact-pressure roller is deflected, actuates a switch that turns off the drive for the plate cylinder.
A disadvantage of the device disclosed in the aforementioned published German Patent Document DE 42 18 602 A1 is that the force causing the deflection of the contact-pressure roller increases as the distance traversed in the deflection increases, and can exceed an allowable distance; another disadvantage is that this force is exerted constantly on the foreign member, i.e., a finger or hand, for example.